The Effects of Extracellular K+, Na+ and Ca++ on Lysosomal Enzyme Secretion from Polymorphonuclear Leukocytes

Abstract

Release of the lysosomal enzymes, lysozyme and β-glucuronidase, from rabbit peritoneal polymorphonuclear leukocytes induced by three kinds of secretogogues, chemotactic factors in the presence of cytochalasin B, the K⁺ ionophore, valinomycin, and the Ca⁺⁺ ionophore, A23187 is profoundly affected by the presence and level of K⁺, Na, and Ca⁺⁺ in the extracellular medium. K⁺ approximately doubles the ability of all chemotactic factors to release in the presence of cytochalasin B. Ouabain, except in a minority of instances, does not prevent enhancement by K⁺ suggesting that the enhancement is not due to activation of the Na⁺,K⁺ pump. Other monovalent cations can substitute for K⁺ but with less efficiency. Removing Na⁺ from the medium increased spontaneous release in the presence of Ca⁺⁺ but to a much lesser extent in its absence. Chemotactic factor-stimulated release is depressed in the absence of Na⁺. The K⁺ ionophore, valinomycin, has no effect on chemotactic factor-stimulated release; however, it is capable of inducing release by itself. The secretogogue action of valinomycin requires the presence of Ca⁺⁺ and is enhanced by cytochalasin B or K⁺. Nigericin, another K⁺ ionophore, in noncytotoxic concentrations is without effect on release. The enhancing effect of Ca⁺⁺ on release by chemotactic factors and cytochalasin B was confirmed. La⁺⁺⁺ has two effects on release; at sufficiently low concentrations it inhibits the Ca⁺⁺-dependent release induced by chemotactic factors. At concentrations above 10^-5 M, it can sustain chemotactic factor-dependent release in the presence or absence of Ca⁺⁺. The release induced by the Ca⁺⁺ ionophore A23187 requires Ca⁺⁺ and is enhanced by cytochalasin B and by K⁺. The results obtained attest to the central role of external Ca⁺⁺ in the induced secretion of lysosomal enzymes from the neutrophil. It is suggested that all three kinds of secretogogues induce release by causing an influx of Ca⁺⁺ into the cytoplasm of the PMN. Cytochalasin B and K⁺ are believed to exert their effects by increasing the rate or extent of the hypothesized Ca⁺⁺ influx.